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 Forum index » DIY Hardware and Software » fonik's place
T. H. vco & lfo troubleshooting
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flab



Joined: Feb 13, 2012
Posts: 60
Location: Glasgow

PostPosted: Thu Jul 18, 2013 7:36 am    Post subject: T. H. vco & lfo troubleshooting Reply with quote  Mark this post and the followings unread

well last week i finished building those nice red pcbs (555 vco & lfo thomas henry)by fonik - i have to admit that they give me nightmares since then - im testing the boards since last week , i cant really find a problem but there is one

about the vco i have no sound and my 074s are overheating more than the usual

and about the lfo i changed the P FET 5461 with the 2n3820 taking notice the legs position , yet no good with the lfo

from where to start with my troubleshooting

appreciate in advance
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bod



Joined: Apr 28, 2009
Posts: 144
Location: Glasgow

PostPosted: Thu Jul 25, 2013 4:39 am    Post subject: Reply with quote  Mark this post and the followings unread

aha! a fellow Weegie synth fiend! where abouts are you mate?

as for trouble shooting, are you using the Euro pcbs for the pots and sockets? if so i'd check on the orientation of the sockets etc just to make sure, then the polarity of the PSU connections, and any caps that have a specific polarity orientation.

have you got an osciloscope? and if so, can you get any sort or waveforms? i havent built mine as yet, but this is where id start.
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roglok



Joined: Aug 28, 2010
Posts: 156
Location: uptown

PostPosted: Thu Jul 25, 2013 5:50 am    Post subject: Reply with quote  Mark this post and the followings unread

just a wild guess, but are you using a CMOS version of the 555 ?
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flab



Joined: Feb 13, 2012
Posts: 60
Location: Glasgow

PostPosted: Mon Jul 29, 2013 3:33 am    Post subject: Reply with quote  Mark this post and the followings unread

hey ,
cheers for answering people-

well Bob im not using the Euro pcbs for the pots and sockets, but i think the orientation of the pot and the jacks are fine - psu connections and caps looking ok as well , on think is i m using jumpers instead of ferrite bread or small res. this could be the answer for the overheating vco - but still jjust for that, i dont really have an oscilloscope, im using one from time to time its a bit hard to get some numbers right now

Roglok i do use the cmos of the 555 version , but even if i didnt thats not really critical, they just perform in a different way
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fonik



Joined: Jun 07, 2006
Posts: 3721
Location: Germany
Audio files: 23

PostPosted: Tue Jul 30, 2013 5:49 am    Post subject: Re: T. H. vco & lfo troubleshooting Reply with quote  Mark this post and the followings unread

soory for the late reply. been on a two weeks vacation w/o internet access.

flab wrote:
about the vco i have no sound and my 074s are overheating more than the usual

before checking anything else i would take care about the hot 074s.
maybe there is a short?
maybe some ICs got damaged already? replace them.
disconenct the module from the PSU and measure the resistance between the rails and GND.

Quote:
and about the lfo i changed the P FET 5461 with the 2n3820 taking notice the legs position , yet no good with the lfo

to get it started, start with the LFOs core (integrator/comparator around IC1):
what does the P-Fet do? it shorts out the timing cap of the LFOs integrator (IC1A). so if you just leave it off you should see a nice triangle at IC1 pin 7. to be sure you should set R57 (Rate) to mid position, since it might stall whan fully CCW.

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flab



Joined: Feb 13, 2012
Posts: 60
Location: Glasgow

PostPosted: Mon Aug 12, 2013 10:36 am    Post subject: Reply with quote  Mark this post and the followings unread

hiya ,
thanks for answering back and sorry for the late response

well I spend some time messing with these modules the other days , and I made some progress with the LFO
I have output now for saw - tri - pulse but yet i cant the a sine one

about the VCO now so far no good - I did changed all the ICs with no differences , still getting mega hot
also how can i use the measurements of the resistance between rails and GND?

cheers
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rosch



Joined: Oct 03, 2009
Posts: 159
Location: germany

PostPosted: Sat Aug 17, 2013 12:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

you can measure continuity (or resistance) between the rails and GND. if the value is something around 0 ohms there is a short in that section.
you shouldn't put in ICs until you are sure there is no short anymore. if the first ics were destroyed it might have happened to the new ones too.
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